What Are the Parts of the Ear?
The ear has three main parts: the outer ear (including the external auditory canal), middle ear, and inner ear. The outer ear (the part you can see) opens into the ear canal. The eardrum (tympanic membrane) separates the ear canal from the middle ear. The middle ear contains three small bones which help amplify and transfer sound to the inner ear.
These three bones, or ossicles, are called the malleus, the incus, and the stapes (also referred to as the hammer, the anvil, and the stirrup respectively). The inner ear contains the cochlea which changes sound into neurological signals and the auditory (hearing) nerve, which takes sound to the brain.
How Do Ears Transmit Sound to the Brain?
Any source of sound sends vibrations or sound waves into the air. These funnel through the ear opening, down the external ear canal, and strike your eardrum, causing it to vibrate. The vibrations are passed to the three small bones of the middle ear, which transmit them to the cochlea. The cochlea contains tubes filled with fluid. Inside one of the tubes, tiny hair cells pcik up the vibrations and convert them into nerve impulses. These impulses are delivered to the brain via the hearing nerve. The brain interprets the impulses as sound (music, voice, a car horn, etc.).
How Is Sound Measured?
Decibels (dB) measure the intensity of sound. The scale runs from the faintest sound the human ear can detect, which is labeled 0 dB, to more than 180 dB, the noise at a rocket pad during launch. Most experts agree that continual exposure to more than 85 decibels is dangerous. Recent studies show an alarming increase in noise-related hearing loss in young people.
Approximate examples of decibel levels:
- Faintest sound heard by human ear – 0 dB
- Whisper, quiet library – 30 dB
- Normal conversation, sewing machine, typewriter – 60 dB
- Lawnmower, shop tools, truck traffic – 90 dB
- Chainsaw, pneumatic drill, snowmobile – 100 dB
- Sandblasting, loud rock concert, auto horn – 115 dB
- Gun muzzle blast, jet engine (such noise can cause pain and even brief exposure injures unprotected ears) – 149 dB
- The Occupational Safety and Health Administration’s limit for noise without hearing protectors – 140 dB
What Is Pitch?
Pitch is the frequency of sound vibrations per second measured in hertz or kilohertz, and duration. A low pitch, such as a deep voice or a tuba, makes fewer vibrations per second than a high voice or violin—the higher the pitch, the higher the frequency. Loss of high-frequency hearing also can make speech sound muffled.
What Causes Hearing Loss?
The ear has three main parts: the outer, middle, and inner ear. The outer ear (the part you can see) opens into the ear canal. The eardrum separates the ear canal from the middle ear. Small bones in the middle ear help transfer sound vibrations to the inner ear. Here, the vibrations become nerve impulses, which the brain interprets as music, a slamming door, a voice, and so on.
When noise is too loud, it begins to kill the nerve endings in the inner ear. Prolonged exposure to loud noise destroys nerve endings. As the number of nerve endings decreases, so does your hearing. There is no way to restore life to dead nerve endings; the damage is permanent. The longer you are exposed to a loud noise, the more damaging it may be. Also, the closer you are to the source of intense noise, the more damaging it is.
How Does Noise Exposure Cause Hearing Loss?
Very loud sounds damage the inner ear by damaging the hair cells of the cochlea. When loud sounds are exposed to the ear for a short time, one may experience what’s called a temporary threshold shift, or a temporary hearing loss. This hearing loss may be accompanied by tinnitus (a ringing in the ears). One may recover from the temporary loss. But if the ear is exposed to loud sounds over longer periods of time, the hair cells can be permanently damaged, causing permanent sensorineural hearing loss.
How Can I Tell if a Noise Is Dangerous?
People differ in their sensitivity to noise. As a general rule, noise may damage your hearing if you are at arm’s length and have to shout to make yourself heard. If noise is hurting your ears, your ears may ring, or you may have difficulty hearing for several hours after exposure to the noise. Noise is characterized by intensity, measured in decibels; pitch, measured in hertz or kilohertz; and duration.
Can Noise Affect More Than My Hearing?
A ringing in the ears, called tinnitus, commonly occurs after noise exposure, and often becomes permanent. Some people react to loud noise with anxiety and irritability, an increase in pulse rate and blood pressure, or an increase in stomach acid. Very loud noise can reduce efficiency in performing difficult tasks by diverting attention from the job.
How Can I Protect Myself Against Noise?
Wear hearing protectors, especially if you must work in an excessively noisy environment. You should also wear them when using power tools, noisy yard equipment, or firearms, or riding a motorcycle or snowmobile. Hearing protectors come in two forms: earplugs and earmuffs.
Earplugs are small inserts that fit into the outer ear canal. They must be sealed snugly so the entire circumference of the ear canal is blocked. An improperly fitted, dirty, or worn-out plug may not seal properly and can result in irritation of the ear canal. Plugs are available in a variety of shapes and sizes to fit individual ear canals and can be custom-made. For people who have trouble keeping them in their ears, the plugs can be fitted to a headband.
Earmuffs fit over the entire outer ear to form an air seal so the entire circumference of the ear canal is blocked, and they are held in place by an adjustable band. Earmuffs will not seal around eyeglasses or long hair, and the adjustable headband tension must be sufficient to hold earmuffs firmly in place.
Earplugs and earmuffs can be found at most pharmacies.
Will I Hear Other People and Machine Problems if I Wear Hearing Protectors?
Just as sunglasses help vision in very bright light, so hearing protectors enhance speech understanding in very noisy places. Even in a quiet setting, a normal-hearing person wearing hearing protectors should be able to understand a regular conversation.
Hearing protectors do slightly reduce the ability of those with damaged hearing or poor comprehension of language to understand normal conversation. However, it is essential that persons with impaired hearing wear earplugs or muffs to prevent further inner ear damage in very noisy places.
It has been argued that hearing protectors might reduce a worker’s ability to hear the noises that signify an improperly functioning machine. However, most workers readily adjust to the quieter sounds and can still detect such problems. If a worker is already hearing impaired, he or she needs expert advice about how to protect against further damage. In some cases hearing aids can and should be used under earmuffs.
How Can I Tell if My Hearing Is Damaged?
Hearing loss usually develops over a period of several years. Because it is painless and gradual, you might not notice it. What you might notice is a ringing or other sound in your ear (tinnitus), which could be the result of long-term exposure to noise that has damaged hearing nerves. Or you may have trouble understanding what people say; they may seem to be mumbling, especially when you are in a noisy place such as a crowd or a party. This could be the beginning of high-frequency hearing loss; a hearing test will detect it.
If you have any of these symptoms, they may be caused by impacted wax or an ear infection, which are relatively easy to correct. However, you may suffer from noise-related hearing loss. In any case, take no chances with noise—the hearing loss it causes is permanent. If you suspect hearing loss, consult a physician with special training in ear care and hearing disorders (called an otolaryngologist or otologist). This doctor can diagnose your hearing problem and recommend the best way to manage it. For more information on the laws for on-the-job noise exposure, please refer to the information provided at www.entnet.org.
Should MP3 Player Use Be Limited?
The maximum sound from an iPod Shuffle has been measured at 115 decibels, a level that can cause hearing loss to listeners of all ages. A survey sponsored by the Australian government found that about 25 percent of people using portable stereos had daily noise exposures high enough to cause hearing damage. Further research from the Netherlands reports that 90 percent of adolescents listened to music through earphones on MP3 players, almost half used high-volume settings, and only 7 percent used a noise limiter.
Researchers at Boston Children’s Hospital determined that listening to a portable music player with headphones at 60 percent of their potential volume for one hour a day is relatively safe. The maximum volume limit is adjustable on many current MP3 players.
Why Are Earplugs Important at Concerts?
Parents should be aware that various medical studies have found sound levels at rock concerts often to be significantly higher than 85 dBA, with some reports suggesting that sound intensity may reach 90 dBA to as high as 122 dBA.
To experience 85 dBA, listen to an electric shaver or a busy urban street. If levels are maintained at values greater than 85 dBA for long periods of time, this may lead to a significant noise exposure. Frequent concertgoers may experience some potentially irreversible hearing loss from their experience.
A research study, “Incidence of spontaneous hearing threshold shifts during modern concert performances” (Opperman, Reifman, Schlauch, Levine; Otol-HNS 2006, 134:4: 667-673), examined sound intensity throughout a well known concert venue, and the effectiveness of earplugs. The findings stated that sound pressure levels appeared equally hazardous in all parts of the concert hall, regardless of the type of music played. Accordingly, you should use earplugs at every type of musical concert, regardless of your distance to the stage.
A good rule of thumb: When a child accompanies a parent to any activity or location with excessive noise, ear protection should be worn by the entire family.